In general, an integrated circuit (also referred to as a chip or microchip) can be used to process digital or analogue signals. An integrated circuit may include a plurality of electrical components whose electrical circuitry is configured according to one or more functions of the integrated circuit. For example, by means of the electrical components of an integrated circuit signals can be processed or switching operations can be carried out. Certain fields of use may make it necessary to use an integrated circuit to process electrical voltages or signals which exceed the electrical loading capacity (e.g. breakdown voltage) of the individual electrical components. Alternatively or additionally, miniaturization of the electrical components can bring about a reduction in their electrical loading capacity, with the result that the maximum voltage with which the integrated circuit can be operated is reduced. The increasing tendency in the field of electronic circuits of promoting the miniaturization of said circuits can bring about a situation in which the electrical components can no longer satisfy the requirements which are made of the electrical loading capacity with increasing miniaturization. This can be compensated only by modifying the electrical components, e.g. by means of additional masks, which increases the production costs.
Conventionally, it is possible to use what is referred to as a cascode circuit (not to be confused with a cascade) in which a plurality of electrical switches divide the electrical load (cf. FIG. 1), e.g. a plurality of transistors M1, M2, M3. The cascode circuit can be regulated by means of a switch S1, with the result that said cascode circuit is kept operational as far as possible independently of the input voltage Vin (also referred to as an active cascode circuit). The active cascode circuit requires an additional auxiliary voltage VDDnom in order to permit switching above the threshold voltage Vth. If the drain terminal voltage of M3 is lower than VDDnom−Vth, S1 can be switched to a conductive stage and the gate terminal of M3 can be connected to VDDnom, with the result that M3 is kept operational. For voltages higher than VDDnom+Vth, S2 can be in the conductive state and M3 can be operated as a diode. However, owing to an absence of overdriving, a diode does not have low impedance, for which reason large resistive losses have to be accepted. In addition, the cascode circuit has a switching gap between VDDnom−Vth and VDDnom+Vth in which, e.g. if the drain terminal of M3 is connected to VDDnom, none of the two switches S1 and S2 is closed, with the result that the gate terminal of M3 is floating. In addition, the active controller S1, S2 increases the complexity of the cascode circuit if the number of cascode stages is increased, with the result that said circuit is no longer practical. Therefore, the maximum voltage Vin which can be switched by means of the cascode circuit in an economical way is limited.
A passive cascode circuit (cf. FIG. 2) uses a voltage divider R1, R2, R3, R4, R5 for switching the transistors. The voltage present at the transistors M1, M2, M3, M4, M5 is made available in a passive fashion, i.e. is divided off from the input voltage Vin by means of the voltage divider. By means of the passive cascode circuit it is then possible to dispense with the additional supply voltage VDDnom, which simplifies the design. Therefore, further transistors can be added to the passive cascode circuit without having to change their design. Therefore, the passive cascode circuit can be implemented with less expenditure and significantly more transistors M1, M2, M3, M4, M5 than the active cascode circuit, for which reason the passive cascode circuit is suitable, in particular, for high voltages. However, large values for the gate-source voltage and the gate-drain voltage have to be accepted, which increases the required loading capacity of the transistors M1, M2, M3, M4, M5.
The active cascode circuit is conventionally used if a high level of reliability is significant. In contrast to this, the passive cascode circuit is used if a high voltage to be switched is significant.